System and method for compensating for potential and current transformers in energy meters

ABSTRACT

A meter device for measuring electrical energy is provided. The meter device includes circuitry for measuring at least one parameter of electrical energy provided to the meter device. A storage device is provided for storing at least one calibration factor for compensating for errors associated with at least one of at least one external current transformer (CT) and at least one external potential transformer (PT) that operates on the electrical energy provided to the meter device. At least one processor is provided for processing the at least one calibration factor for adjusting the measuring for compensating for the errors when measuring the at least one parameter of electrical energy.

This application is a continuation application of an application filedon Apr. 18, 2005, assigned U.S. application Ser. No. 11/109,351,entitled “System and Method for Compensating for Potential and CurrentTransformers in Energy Meters”, and which claims priority under 35U.S.C. §119 to U.S. Provisional Application Ser. No. 60/619,909, filedon Oct. 18, 2004, and entitled “Potential Transformer and CurrentTransformer Calibration for Revenue Meters”, the entire contents of bothapplications are expressly incorporated herein in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to meters for measuring energy. In particular,this invention relates to a system and method for compensating forpotential and current transformers in meters for measuring energy.

2. Description of the Related Art

Electrical utility companies (“utilities”) track electric usage bycustomers by; using power meters. These meters track the amount of powerconsumed at a particular location, such as a substation. The electricutility companies may use the power meter to charge its customers fortheir power consumption, i.e., revenue metering.

Traditionally, power meters used mechanical means to track the amount ofconsumed power. The inductive spinning disk power meter is stillcommonly used. The spinning disk drives mechanical counters that trackthe power consumption information.

Newer to the market are electronic power meters. Electronic meters havereplaced the older mechanical meters, and utilize digital sampling ofthe voltage and current waveforms to generate power consumptioninformation. In both, the mechanical and electronic power meters, whenused with high voltages and currents, such as at a substation setting,the meters incorporate external sensors to divide the voltage andcurrent into levels that are safe for the meters to read. Typically, aprimary voltage is divided to a secondary 120 volt waveform, and aprimary current is divided to a 5 amp secondary waveform. The sensorsare current and/or voltage (potential) transformers, which introduceerrors into the measurements in addition to errors introduced by othersources, such as the meters themselves. Furthermore, errors introducedby the current transformers are nonlinear throughout the range ofmagnitude of usage. Additionally, the current transformers are inductiveby nature, and generate a phase shift which further degrades accuracy inmeasurements.

Therefore, it is an aspect of the invention to compensate for errorsintroduced by current and/or voltage transformers into readings by powermeters.

It is further an aspect of the invention to compensate for nonlinearerrors introduced by current transformers into readings by power meters.

Additionally, it is an aspect of the invention to compensate for errorsintroduced into readings by power meters due to phase shifts generatedby the current transformers.

SUMMARY OF THE INVENTION

A meter device for measuring electrical energy is provided. The meterdevice includes circuitry for measuring at least one parameter ofelectrical energy provided to the meter device and a storage device forstoring at least one calibration factor for compensating for errorsassociated with at least one of at least one external currenttransformer (CT) and at least one external potential transformer (PT)that operates on the electrical energy provided to the meter device. Themeter device further includes at least one processor for processing theat least one calibration factor for adjusting the measuring forcompensating for the errors when measuring the at least one parameter ofelectrical energy.

Pursuant to another embodiment of the disclosure, calibration factors ofthe at least one calibration factor correct for errors measured duringtesting of respective test points of a series of test points, wherein atleast one calibration factor corresponds to each test point. Each testpoint corresponds to a different current magnitude for modelingnon-linearity of errors associated with a range of current magnitudesfor current signals of the electrical energy operated on by the at leastone external CT, wherein the greater the non-linearity of the errors,the greater the concentration of test points.

In another embodiment of the disclosure a method is provided formeasuring electrical energy in a meter. The method includes the step ofstoring at least one calibration factor for compensating for errorsassociated with at least one of at least one CT and at least one PT thatoperates on electrical energy provided to the meter device. The methodfurther includes the step of measuring at least one electrical parameterof electrical energy provided to the meter device. The measuringincludes adjusting the measuring for compensating for the errors,including processing the measured at least one electrical parameterusing the at least one calibration factor. Calibration factors of the atleast one calibration factor correct for errors measured during testingof respective test points of a series of test points, wherein at leastone calibration factor corresponds to each test point. Each test pointcorresponds to a different current magnitude for modeling non-linearityof errors associated with a range of current magnitudes for currentsignals of the electrical energy operated on by the at least one CT,wherein the greater the non-linearity of the errors, the greater theconcentration of test points.

In a further embodiment of the disclosure, a processing device isprovided in communication with the meter device, where the meter devicemeasures electrical energy. The processing device includes an inputdevice for receiving input information relating to at least one error,where an error of the at least one error is related to a differencebetween an input value corresponding to at least one of voltage,current, and phase shift therebetween associated with electrical energyoperated on by at least one of at least one external CT and at least oneexternal PT which is provided to the meter device, and a value measuredby the meter device which corresponds to the input value. The processingdevice further includes at least one processor for generating at leastone calibration factor, each calibration factor corresponding to anerror of the at least one error for adjusting measurement by the meterdevice in accordance with the errors; and at least one communicationdevice for uploading at least one of the generated calibration factorsto the meter device.

Pursuant to another embodiment of the disclosure, the at least one erroris determined by performing a test, including measuring energyassociated with a series of at least two test points. Each test point ofthe series corresponds to a different input current value over a rangeof input current values of the electrical energy operated on by the atleast one CT. For each test point of the series of at least two testpoints there is at least one corresponding calibration factor.Respective calibration factors provide for adjusting measurement by themeter device, including correcting for errors of the at least one errorrelated to the input current values to which the respective test pointscorrespond. The calibration factors corresponding to the respective testpoints compensate for non-linearity of the at least one error associatedwith the range of input current values.

In another embodiment of the disclosure, a method is provided forcalibrating the meter device for measuring electrical energy. The methodincludes the step of receiving information relating to at least oneerror, wherein each error of the at least one error is related to adifference between a respective input value corresponding to at leastone of voltage, current, and phase shift therebetween associated withpower operated on by at least one of at least one CT and at least one PTwhich is provided to the meter device, and a value measured by the meterdevice which corresponds to the input value. The method further includesthe steps of generating at least one calibration factor, eachcalibration factor corresponding to an error of the at least one errorfor adjusting measurement by the meter device in accordance with theerror, and uploading generated calibration factors to the meter device.The at least one error is determined by performing a test, includingmeasuring energy associated with a series of at least two test points.Each test point of the series corresponds to a different input currentvalue over a range of input current values of the electrical energyoperated on by the at least one CT. For each test point of the seriesthere is at least one corresponding calibration factor. Respectivecalibration factors provide for adjusting measurement by the meterdevice, including correcting for errors of the at least one errorrelated to the input current values to which the respective test pointscorrespond. The calibration factors corresponding to the respective testpoints compensate for non-linearity of the at least one error associatedwith the range of input current values.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments of the invention will be described herein below withreference to the figures wherein:

FIG. 1 is a schematic diagram of a power metering system in a powerdistribution substation in accordance with the present disclosure;

FIG. 2 shows tables for storing calibration factors for voltage gain,current gain and phase compensation;

FIG. 3A is a flow diagram of steps performed during voltage calibrationof an energy meter device of the power metering system shown in FIG. 1;

FIG. 3B is a flow diagram of steps performed during current calibrationof an energy meter device of the power metering system shown in FIG. 1;and

FIG. 3C is a flow diagram of steps performed during phase calibration ofan energy meter device of the power metering system shown in FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings wherein like reference numerals identifysimilar structural elements, there is illustrated in FIG. 1 a meteringsystem 10 for metering power provided to the system 10 in at least onepower line having at least one phase, and typically in three power lineshaving three respective phases, phases A, B and C. The respective powerlines corresponding to phases A, B and C (wherein the power lines areherein referred to as phases A, B and C, respectively) pass through atleast one instrument transformer, including current transformers (CTs)12 and optionally potential (voltage) transformers (PTs) 14, where CTs12A, 12B and 12C correspond to the phases A, B and C, respectively, andPTs 14A, 14B and 14C correspond to the phases A, B and C, respectively.The signals output by the CTs 12 and the PTs 14 (e.g., when PTs 14 areprovided) are provided to an energy meter device 16 which is in wired orwireless communication with a processing device 18. In accordance withthe present disclosure, calibration factors for the CTs 12 and PTs 14are determined and programmed into the meter device 16.

Test equipment 20 is provided for selecting parameters of energy to beprovided at the respective phases. The test equipment 20 is operated bya human operator, a processing device and/or a control unit 22 to selecta desired parameter of the energy, such as current magnitude, voltagemagnitude and/or phase shift. Circuit breaker or fuse devices 24 may beprovided along lines input to and/or output from the PTs 14 forproviding protection to hardware, such as the PTs 14 and/or the meterdevice 16. An optional neutral phase and a neutral (e.g., auxiliary) CT12 may be provided, where the neutral phase is provided as input to theneutral CT 12, and the output is provided as a second input to therespective PTs 14. The output from the PTs 14 which corresponds to theneutral phase may be provided as a voltage reference signal to the meterdevice 16.

The respective CTs 12 provide control and protection by reducing currentflowing through the corresponding power lines for providing a current tothe meter device 16 at a level suitable for the meter device 16 which isproportionate to the current flowing through the power line. The CTs 12further provide electrical isolation of the meter device 16 from thepower line. The power line (e.g., phase A, B or C) passes through therespective CT 12 by entering through a primary side (e.g., high side).The CT 12 converts the magnetic field generated in the power line by thecurrent flowing through the power line into a stepped down currentreduced in accordance with a predetermined ratio. The reduced linecurrent is output through a secondary side (e.g., low side) of the CT 12and provided as a current input to the meter device 16.

The respective PTs 14 step voltage of the corresponding power line downto a level which is safe and manageable for the metering device 16.Typically, a respective PT 14 includes a conventional constant-voltagetransformer with primary and secondary windings on a common coreconnected in shunt or parallel to the corresponding power line. Thesecondary winding insulates the meter device 16 from the power line. Thepower line is provided to the respective PT 14 at a primary side (e.g.,high side), and the stepped down voltage is output from a secondary side(e.g., low side) of the PT 14 and provided as a voltage input to themeter device 16.

The meter device 16 is a meter for calibrating and measuring voltage andcurrent inputs, including compensating for errors associated with theCTs 12 and the PTs 14 in accordance with the present disclosure. Themeter device 16 may be used for measuring electricity usage, such as ina substation, at a customer location, or other location where energymeasurement is required, e.g., for measuring current, voltage, powerand/or usage. A metering device and calibration thereof is described inU.S. Pat. No. 6,735,535, the entire contents of which are expresslyincorporated herein in their entirety. The meter device 16 includes aplurality of current input lines 32 for receiving current inputs, e.g.,which are the outputs from the CTs 12, and a plurality of voltage inputlines 34 for receiving voltage inputs, e.g., which are the outputs fromthe PTs 14. The meter device 16 includes circuitry for processing thecurrents and voltages received at the current input lines 32 and thevoltage input lines 34, respectively. The circuitry may include forexample, at least one amplifying device, sample and hold circuitry,analog to digital converter circuitry, multiplexor device, filtercircuitry, processor, (e.g., a digital signal processor (DSP)), storagedevice (e.g., RAM, ROM, EPROM, flash memory, etc.) or a combinationthereof for processing the received inputs and generating acorresponding measured value. Furthermore, various elements of thecircuitry may be included together. For example, the storage device maybe included with the DSP.

Electrical components of the meter device 16 typically introduce errors(e.g., phase error) into measurements generated by the meter device 16.It is preferable that at the factory a first calibration procedure isperformed in which the meter device 16 is operated in a first mode forcalibrating the meter device 16 for compensating for errors generated bythe meter device 16. When operating in the first mode, errors generatedby the meter device 16 are determined, and meter calibration factors aregenerated which will be used for compensating for errors introduced bythe meter device 16 when the meter device 16 operates in a second modefor operation of the meter device 16 for measuring power. The metercalibration factors may be stored in a storage device of the meterdevice 16, and accessed during operation of the meter device 16. Forexample, the meter calibration factors may be stored in a metercalibration factor table in a storage device such as an EPROM that isaccessible by the processor, e.g., DSP, of the meter device 16.

The meter device 16 may be operated in a third mode in which a secondcalibration procedure is performed for calibrating the meter device 16for compensating for errors generated by the CTs 12 and the PTs 14. Whenoperating in the third mode, errors generated by the CTs 12 and PTs 14are determined, and calibration factors for the CTs and/or PTs aregenerated which will be used for compensating for errors introduced bythe CTs 12 and PTs 14 when the meter device 16 operates in the secondmode during operation of the meter device 16 for measuring power. Thecalibration factors for the CTs and/or PTs (also referred to as CT/PTcalibration factors) may be stored in a storage device of the meterdevice 16, and accessed during operation of the meter device 16. FIG. 2shows CT/PT calibration factor tables 200 in which the CT/PT calibrationfactors may be stored in a storage device such as an EPROM that isaccessible by the processor, e.g., DSP, of the meter device 16. Table202 stores voltage gain calibration factors associated with voltagecompensation, table 204 stores current gain calibration factorsassociated with current compensation with the current and voltagesignals output from the test equipment 20 in phase (or having a unityphase angle), and table 206 stores phase calibration factors associatedwith current compensation with the phase for the current and voltagesignals output from the test equipment 20 having a sixty degree shift.

The meter device 16 preferably further includes meter correction tablesfor storing the meter correction values. The meter device 16 may use themeter correction values when operating in the third mode for calibratingfor CT/PT compensation. Furthermore, the meter correction values arepreferably used during operation of the meter device 16 in conjunctionwith the CT/PT tables 202, 204, 206 when operating in the second modefor performing revenue functions.

The meter device 16 is further provided with at least one connector orport 40 providing input/output (I/O) for communicating with otherdevices, including the processing device 18. Communication may bewireless or wired, such as for connecting to the processing device 18for using a serial protocol, such as RS232 or RS485. The meter device 16may further include a display and/or at least one user input device,such as a keypad. During operation of the meter device 16, the processorof the meter device 16 executes a series of programmable instructionswhich may be stored in the at least one storage device. The mode ofoperation may be selected, such as via user input and/or by theprocessing device 18.

The processing device 18, which may be a device such as personalcomputer or a server, includes at least one input device, such as atleast one I/O connector or port and/or user input device, forcommunicating with the meter device 16, including receiving inputinformation and uploading CT/PT calibration factors to the meter device16. The input information preferably relates to input valuescorresponding to the power input by the test equipment 20 into the CTs12 and/or the PTs 14 and values measured by the meter device 16corresponding to respective input values. The input information may bereceived as user input, from the meter device 16, the test equipment 20and/or another processor or control unit. The processing device 18further includes at least one processor for executing a series ofprogrammable instructions for at least computing the CT/PT calibrationfactors in accordance with a difference between respective input valuesand the corresponding value measured by the meter device 16. The seriesof programmable instructions can be stored on a computer-readablemedium, such as ROM, flash memory, RAM, a hard drive, CD-ROM, smartcard, 3.5″ diskette, etc., or transmitted via propagated signals forbeing executed by the at least one processor for performing thefunctions disclosed herein and to achieve a technical effect inaccordance with the invention.

When operating in the third mode, the second calibration procedure isperformed for generating and storing in the meter device 16 thecalibration factors, including testing at least one test point byoperating test equipment 20 to select a known voltage, current and/orphase as the input to a respective CT 12 and/or PT 14, and measuring theoutput thereof by the meter device 16. The test equipment may becontrolled and/or operated by an operator, a control unit 22 and/orprocessor 18 for automatically or manually stepping through the testpoints and tests. Preferably, the test equipment is accurate and wellcalibrated for providing a laboratory test setting. The secondcalibration procedure is preferably performed when a CT 12 or PT 14 isinstalled with the meter device 16, such as upon setting up a substationor replacing at least one of the CTs 12, PTs 14 and the meter device 16at the substation. The mode of operation for the meter device 16 isselected to be the third mode. The measured output is compared to theexpected output and a corresponding error value is determined, e.g., theratio of the difference between the measured value and the expectedvalue with respect to the expected value. The comparison between themeasured and expected values and the determination of the error may beperformed by an operator, another device (e.g., a remote device) and/orthe processing device 18. If not determined by the processing device 18,the error is provided to the processing device 18. The processing device18 determines adjustments for compensating for the error at the testpoint, after which the adjustments are written into the appropriatetable 202, 204 or 206 of the measuring device 16 as CT/PT calibrationfactors. The procedure is repeated for testing a series of test points,where the test equipment 20 is operated to adjust one of the selectedvoltage, current or phase angle for each repetition.

With respect to FIGS. 3A-3C, an exemplary method is illustrated, inwhich a second calibration procedure is performed, including a voltagecompensation test, followed by a first power (or gain) compensation testwith phase angle at unity (e.g., voltage and current signals in phase),followed by a second power (or phase) compensation test with phase tohave a selected lag, such as 60 degrees, however the method of thedisclosure is not limited to the described order or combination oftests, and a subset of the tests may be used. A user interface isprovided with the processing device 18 to facilitate the process ofcalibrating the meter device 16. Furthermore, the method described usesa direct adjustment interface at the processing device 18 for readingand writing information into the meter device 16, e.g., for reading andmodifying registers of the meter device 16.

With reference to FIG. 3A, the voltage compensation test is performedusing the corresponding PTs 14, without using the CTs 12. If the PTs 14are not included, this step may be omitted. The voltage compensationtest begins at step 301 by operating the test equipment 20 to provide aselected voltage, preferably 120V, as the input to each of the PTs 14A,14B and 14C. At step 302, the measured voltage magnitude is compared tothe expected voltage magnitude and the error is determined. The errormay be determined by the processing device 18 and/or entered into theprocessing device 18, e.g., entered into a software program executed bythe processing device 18. At step 303, the processing device 18 (e.g., asoftware program executed by the processing device 18) computes theadjustments for performing the compensation in accordance with thedetermined error and generates corresponding voltage gain calibrationfactors. At step 304, the voltage gain calibration factors are uploadedfrom the processing device 18 and written into the meter device (MD) 16for updating table 202, which may include modifying the appropriateregisters. The PTs 14 function linearly and do not generate asubstantial phase shift. Accordingly, compensations determined by onetest point of the voltage compensation test is typically sufficient forcompensating throughout the range of use of the PTs 14.

With respect to FIG. 3B, the first power compensation test is performedusing the corresponding CTs 12 and PTs 14 (or only the CTs 12) withphase angle at unity for calibrating the meter device 16 to compensatefor magnitude. The first power compensation test starts at step 305 byoperating the test equipment 20 at a first test point to provide aselected current, shown in the present example as 5 amps. At step 306,the measured current magnitude is compared to the expected currentmagnitude, and the error for the first test point is determined by theprocessing device 18 and/or entered into the processing device 18. Atstep 307, the processing device 18 computes the adjustments forperforming the compensation in accordance with the determined error andgenerates corresponding current gain calibration factors. At step 308,the current gain calibration factors are uploaded from the processingdevice 18 and written into the meter device 16 for updating table 204,which may include modifying the appropriate registers. At step 309, thetest equipment 20 is operated at a second test point to provide aselected current, where the selected current has been changed relativeto the previous test point. In the current example, the selected currentfor the second test point is decremented relative to the first testpoint to 2.5 amps. In steps 310-312, the error and current phasecalibration factor for compensating for the second test point arecomputed and uploaded to the meter device 16.

In steps 313-328, compensation at subsequent test points is performed.In the present example, the currents corresponding to subsequent testpoints are selected to be 1.0 amps, 0.5 amps, 0.25 amps and 0.15 amps,respectively, however the present disclosure is not limited thereto, andother currents may be selected, a different number of test points may beused, the current may be increased or decreased for subsequent testpoints, the intervals between selected currents for adjacent test pointsmay be larger or smaller than the example shown, etc. The error andcurrent gain correction factors for the respective test points arecomputed and uploaded to the meter device 16. The multiple test pointsprovide the function of adjusting for non-linearity of the CTs 12 anderrors generated by the CTs 12. More particularly, the non-linearity ofthe CTs 12 is more severe at low levels of current, e.g., for 0-5 amps,after which the CTs 12 operate more linearly. Accordingly, it ispreferable to have closely spaced test points for the lower currents formodeling small linear curves in-between the test points.

With reference to FIG. 3C, the second power compensation test isperformed using the corresponding CTs 12 and PTs 14 with phase having asixty degree lag (e.g., a 0.5 power factor (PF) for sinusoidal currentand voltage signals) for calibrating the meter device to compensate forphase shift. The second power compensation test starts at step 329 byoperating the test equipment 20 at a first test point to provide aselected current, shown in the present example as 10 amps. At step 330,the measured phase angle is compared to the expected phase angle and theerror for the first test point is determined by the processing device 18and/or entered into the processing device 18. At step 331, theprocessing device 18 computes the adjustments for performing thecompensation in accordance with the determined error and generatingcorresponding phase calibration factors. At step 332, the phasecalibration factors are uploaded from the processing device 18 andwritten into the meter device 16 for updating table 206, which mayinclude modifying the appropriate registers. At step 333, the testequipment 20 is operated at a second test point to provide a selectedcurrent, where the selected current has been changed relative to theprevious test point. In the current example, the selected current forthe second test point is decremented relative to the first test point to5 amps. In steps 334-336, the error and phase calibration factors forcompensating for the second test point are computed and uploaded to themeter device 16.

In steps 337-348, compensation at subsequent test points is performed.In the present example, the currents corresponding to subsequent testpoints are selected to be 2.5 amps, 1.0 amps and 0.5 amps, respectively,however the present disclosure is not limited thereto, and othercurrents may be selected as described above. The error and adjustmentsfor compensating for the respective test points are computed anduploaded to the meter device 16. The multiple test points provide thefunction of adjusting for non-linearity of the CTs 12 and errorsgenerated by the CTs 12, with a higher concentration of test pointsprovided for lower currents, as discussed above.

When operating in the third mode, another method may be employed forperforming the second calibration procedure which includes using testparameters to automatically step through a series of test points fordetermining error and CT/PT calibration factors which correspond to therespective test points. The test parameters may be user entered (e.g.,for entering individual parameters), user selected (e.g., for selectinga group of parameters) and/or entered or selected by the processingdevice 18 and/or another processing device, such as upon detection of apredetermined condition. The test parameters may include an initialvalue for at least one input value selected from an input voltage, aninput current which is in phase with the input voltage and/or an inputcurrent at a selected phase shift (e.g., sixty degrees) with respect tothe input voltage; a range for each initial value, and an increment (ordecrement) factor. The second calibration procedure includes for eachinitial input value, setting the test equipment to correlate to theinput value and testing a test point corresponding to the input value,including computing the error, generating the CT/PT calibration factorand storing the CT/PT calibration factor in the meter device 16. Theinitial input value is incremented in accordance with the increment (ordecrement) factor for generating a new input value until the range hasbeen exhausted. A test point is tested for each input value. The settingof the test equipment 20 may be prompted by the processing device 18and/or controlled by the processing device 18.

The increment value may be an absolute or relative value. It is alsocontemplated that instead of using an increment value to determine thenext input value for a test point, a series of input values are providedand each test point is tested by selecting an input value from theseries of input values, where preferably the input value is selected ina sequential order.

Upon each occurrence that the tables 202, 204 or 206 are modified, it ispreferable that an associated time stamp is generated for marking thetime and/or date that the modification was made. Preferably, an operatormay access the time stamp for determining when a previous modificationwas made. A checksum procedure may be performed as well for respectivemodifications for maximizing accuracy.

It is contemplated that uploading may occur after each point is testedor after a group of test points is tested, which may be all of the testpoints or some of the test points. It is further contemplated that thesecond calibration procedure or a portion thereof be repeated afterCT/PT calibration factors corresponding to all of the test points areuploaded for re-resting test points using the most recently added CT/PTcalibration factors.

Once the CT/PT calibration factor tables 200 include one or more entriesthey may be used for compensation during operation of the meter device16. Until then, compensation is not performed or default values (e.g.,in which the calibration factors are set to “one”) are used forperforming compensation without actually correcting or adjusting thevalues read by the meter.

The voltage gain calibration factors stored in table 202 providecorrection to voltage gain of the corresponding phase being read by themeter device 16, and are implemented as divisive factors. Duringoperation of the meter device 16, sampled voltage readings are dividedby the voltage gain calibration factor for adjusting the magnitude ofthe sampled voltage reading. During testing for determining errorscorresponding to CTs 12 and PTs 14, if it is determined that the voltagereading is “y” percent below the expected value, then the voltagereading is increased, which is accomplished by decreasing the voltagegain calibration factor (having a default value of one) by multiplyingthe voltage gain calibration factor by (100/(100+y)).

The current gain calibration factors stored in table 204 providecorrection to current gain readings of the corresponding phase beingread by meter device 16, and are implemented as multiplicative factors.Current gain calibration factors corresponding to several test pointsare provided. During operation of the meter device 16, sampled currentreadings are multiplied by the current gain calibration factor foradjusting the magnitude of the sampled current reading. When a currentreading falls between two test points, the current gain calibrationfactor to use for adjusting the current reading is interpolated betweenthe bounding test points. For example, for a current gain reading forPhase A of 1.75 amps, the current gain calibration is calculated bycompensating in accordance with the current gain calibration factorassociated with the test point 1.0 amps which is stored in field 209(referred to as comp(field 209)) and the test point 2.5 amps which isstored in field 208 (e.g., comp (field 208)). More particularly, thecurrent gain reading is adjusted by multiplying the current reading by((0.5*comp(field 209))+(0.5*(comp(field 208))). Similarly, when themeter device 16 reads a current gain for Phase A of 1.5 amps, thereading is adjusted by multiplying the current reading by((0.33*(comp(field 208))+(0.67*comp(field 207))).

During testing for determining errors corresponding to CTs 12 and PTs14, if it is determined that the current reading is “y” percent lowerthan the expected value, the current reading is increased, which isaccomplished by increasing the current gain calibration factor (having adefault value of one) by multiplying the current gain calibration factorby ((100+y)/100).

The phase calibration factors stored in table 206 provide correction tophase angle readings of the corresponding phase A, B or C being read bymeter device 16. The phase calibration factors are implemented as powerfactor shifts for adjusting the power factor slightly in order to changethe Watt/VA relationship. Phase calibration factors corresponding toseveral test points are provided. During operation of the meter device16, sampled power readings are multiplied by the phase calibrationfactor for adjusting the phase of the sampled power reading. When acurrent reading falls between two test points, the phase calibrationfactor to use for adjusting the phase angle of the power reading isinterpolated between the bounding test points. During testing fordetermining errors corresponding to CTs 12 and PTs 14, if it isdetermined that the power reading is “y” percent below the expectedvalue, then the phase angle (i.e. phase shift) is adjusted, which isaccomplished by shifting the phase calibration factor (having a defaultvalue of 0 degrees) by an additional (cos⁻¹(50/(100+y))) degrees.

Advantageously, corrections provided by the calibration factorscompensate for non-linearity of errors associated with a range ofcurrent magnitudes for current signals of the electrical energy operatedon by the at least one CT 12. The errors are related to a differencebetween an input value corresponding to at least one of voltage,current, and phase shift therebetween associated with electrical energyoperated on by the CTs 12 and provided to the meter device, and a valuemeasured by the meter device 16 which corresponds to the input value.Specifically, the phase and voltage calibration factor correct forerrors measured during testing of respective test points of a series oftest points. Each test point corresponds to a different current value(e.g., magnitude) for modeling non-linearity of errors associated withthe CTs 12. The test points are more closely spaced (e.g., concentrated)for current values where the non-linearity of errors generated isexpected to be greatest or determined to be greatest during testing.

The described embodiments of the present invention are intended to beillustrative rather than restrictive, and are not intended to representevery embodiment of the present invention. Various modifications andvariations can be made without departing from the spirit or scope of theinvention as set forth in the following claims both literally and inequivalents recognized in law.

1. A meter device for measuring electrical energy comprising: circuitryfor measuring at least one parameter of electrical energy monitored bythe meter device; a storage device for storing at least one calibrationfactor for compensating for errors associated with at least one of atleast one external current transformer (CT) and at least one externalpotential transformer (PT) that operates on the electrical energyprovided to the meter device; at least one processor for processing theat least one calibration factor for adjusting the measured at least oneparameter of electrical energy for compensating for the errors whenmeasuring the at least one parameter of electrical energy; and at leastone communication port for receiving the at least one calibration factorfrom an external device.
 2. The meter device according to claim 1,wherein the at least one calibration factor is selected from the groupconsisting of at least one voltage gain calibration factor forcompensating for errors associated with the at least one external PT; atleast one current gain calibration factor for compensating for errorsassociated with the at least one external CT when current and voltagesignals of the electrical energy operated on by the at least oneexternal CT and the at least one external PT, respectively, are inphase; and at least one phase calibration factor for compensating forerrors associated with the at least one external CT with a phase shiftof sixty degrees with respect to the current and voltage signalsoperated on by the at least one external CT and the at least oneexternal PT, respectively.
 3. The meter device according to claim 1,wherein calibration factors of the at least one calibration factorcorrect for errors measured during testing of respective test points ofa series of test points, each test point corresponding to a differentcurrent magnitude for modeling non-linearity of errors associated with arange of current magnitudes for current signals of the electrical energyoperated on by the at least one external CT, and at least onecalibration factor corresponds to each test point.
 4. The meter deviceaccording to claim 3, wherein the greater the non-linearity of theerrors, the greater the concentration of test points.
 5. The meterdevice according to claim 3, wherein at least one calibration factor forthe at least one PT is determined from one voltage test point.
 6. Themeter device according to claim 3, a plurality of phase calibrationfactors are provided, each phase calibration factor corresponding to atest point of the series of test points, wherein compensating for errorswhen measuring power of the at least one parameter of electrical energyin which measured current associated with the measured power falls inbetween two test points includes using a calibration factor related to acalibration factor corresponding to at least one of the two test points.7. The meter device according to claim 1, wherein the at least onecommunication port is further configured for communicating with the atleast one processor.
 8. A method for measuring electrical energy in ameter comprising the steps of: storing at least one calibration factorfor compensating for errors associated with at least one of at least onecurrent transformer (CT) and at least one potential transformer (PT)that operates on electrical energy provided to the meter; and measuringat least one electrical parameter of the electrical energy provided tothe meter device comprising the step of: adjusting the measuring forcompensating for the errors by processing the measured at least oneelectrical parameter using the at least one calibration factor; whereincalibration factors of the at least one calibration factor correct forerrors measured during testing of respective test points of a series oftest points, each test point corresponding to a different currentmagnitude for modeling non-linearity of errors associated with a rangeof current magnitudes for current signals of the electrical energyoperated on by the at least one CT, and at least one calibration factorcorresponds to each test point.
 9. The method according to claim 8,wherein the greater the non-linearity of errors, the greater theconcentration of test points.
 10. The method according to claim 8,wherein the at least one calibration factor is selected from the groupconsisting of at least one voltage gain calibration factor forcompensating for errors associated with the at least one PT; at leastone current gain calibration factor for compensating for errorsassociated with the at least one CT when current and voltage signals ofthe electrical energy operated on by the at least one CT and the atleast one PT, respectively, are in phase; and at least one phasecalibration factor for compensating for errors associated with the atleast one CT with a predetermined non-zero phase shift with respect tothe current and voltage signals operated on by the at least one CT andthe at least one PT, respectively.
 11. The method according to claim 10,wherein compensation is performed by at least one of implementing the atleast one voltage gain calibration factor as a divisive factor,implementing the at least one current gain calibration factor as amultiplicative factor, and shifting a measured phase angle of the atleast one electrical parameter in accordance with the phase calibrationfactor: (the predetermined non-zero phase shift)−(cos⁻¹(50/(100+y))),where “y” is the difference between the measured phase angle and anexpected phase angle, expressed in terms of percentage.
 12. A meterdevice for measuring electrical energy comprising: circuitry formeasuring at least one parameter of electrical energy provided to themeter device; a storage device for storing at least one calibrationfactor for compensating for errors associated with at least one of atleast one external current transformer (CT) and at least one externalpotential transformer (PT) that operates on the electrical energyprovided to the meter device; and at least one processor for processingthe at least one calibration factor for adjusting the measuring forcompensating for the errors when measuring the at least one parameter ofelectrical energy, wherein the at least one calibration factor includesat least one phase calibration factor for compensating for errorsassociated with the at least one external CT with a predetermined phaseshift with respect to the current and voltage signals operated on by theat least one external CT and the at least one external PT, respectively.13. The meter device according to claim 12, wherein during testing fordetermining errors corresponding to the at least one external CT and theat least one external PT, if it is determined that a power reading is“y” percent below an expected value, then the phase shift is adjusted byshifting the at least one phase calibration factor (having a defaultvalue of 0 degrees) by an additional (cos⁻¹(50/(100+y))) degrees. 14.The meter device according to claim 12, wherein the at least onecalibration factor further includes at least one voltage gaincalibration factor for compensating for errors associated with the atleast one external PT, and at least one current gain calibration factorfor compensating for errors associated with the at least one external CTwhen current and voltage signals of the electrical energy operated on bythe at least one external CT and the at least one external PT,respectively, are in phase.
 15. The meter device according to claim 14,wherein calibration factors of the at least one calibration factorcorrect for errors measured during testing of respective test points ofa series of test points, each test point corresponding to a differentcurrent magnitude for modeling non-linearity of errors associated with arange of current magnitudes for current signals of the electrical energyoperated on by the at least one external CT, and at least onecalibration factor.
 16. The meter device according to claim 15, whereinthe greater the non-linearity of the errors, the greater theconcentration of test points, and wherein the non-linearity is greaterat current levels less than 5 amps.
 17. The meter device according toclaim 15, wherein a plurality of current gain calibration factors areprovided, each current gain calibration factor corresponding to a testpoint of the series of test points, wherein compensating for errors whenmeasured current of the at least one parameter of electrical energyfalls in between two test points includes using a calibration factorrelated to a calibration factor corresponding to at least one of the twotest points.
 18. The meter device according to claim 15, a plurality ofphase calibration factors are provided, each phase calibration factorcorresponding to a test point of the series of test points, whereincompensating for errors when measuring power of the at least oneparameter of electrical energy in which measured current associated withthe measured power falls in between two test points includes using acalibration factor related to a calibration factor corresponding to atleast one of the two test points.
 19. A method for measuring electricalenergy in a meter comprising the steps of: storing at least onecalibration factor for compensating for errors associated with at leastone of at least one current transformer (CT) and at least one potentialtransformer (PT) that operates on electrical energy provided to themeter; and measuring at least one electrical parameter of the electricalenergy provided to the meter device comprising the step of: adjustingthe measuring for compensating for the errors by processing the measuredat least one electrical parameter using the at least one calibrationfactor; wherein calibration factors of the at least one calibrationfactor correct for errors measured during testing of respective testpoints of a series of test points, each test point corresponding to adifferent current magnitude for modeling non-linearity of errorsassociated with a range of current magnitudes for current signals of theelectrical energy operated on by the at least one CT, and at least onecalibration factor corresponds to each test point; and wherein thegreater the non-linearity of the errors, the greater the concentrationof test points.
 20. The method according to claim 19, wherein the atleast one calibration factor is selected from the group consisting of atleast one voltage gain calibration factor for compensating for errorsassociated with the at least one PT; at least one current gaincalibration factor for compensating for errors associated with the atleast one CT when current and voltage signals of the electrical energyoperated on by the at least one CT and the at least one PT,respectively, are in phase; and at least one phase calibration factorfor compensating for errors associated with the at least one CT with apredetermined non-zero phase shift with respect to the current andvoltage signals operated on by the at least one CT and the at least onePT, respectively.
 21. The method according to claim 20, whereincompensation is performed by at least one of implementing the at leastone voltage gain calibration factor as a divisive factor, implementingthe at least one current gain calibration factor as a multiplicativefactor, and shifting a measured phase angle of the at least oneelectrical parameter in accordance with the phase calibration factor:(the predetermined non-zero phase shift)−(cos⁻¹(50/(100+y))), where “y”is the difference between the measured phase angle and an expected phaseangle, expressed in terms of percentage.
 22. A processing device incommunication with a meter device for measuring electrical energy, theprocessing device comprising: an input device for receiving inputinformation relating to at least one error, an error of the at least oneerror related to a difference between an input value corresponding to atleast one of voltage, current, and phase shift therebetween associatedwith electrical energy operated on by at least one of at least oneexternal current transformer (CT) and at least one external potentialtransformer (PT) which is provided to the meter device, and a valuemeasured by the meter device which corresponds to the input value; atleast one processor for generating at least one calibration factor, eachcalibration factor corresponding to an error of the at least one errorfor adjusting measurement by the meter device in accordance with theerror; and at least one communication device for uploading generatedcalibration factors to the meter device.
 23. The processing deviceaccording to claim 22, wherein the input information is received fromthe group consisting of a user input device, the meter device, equipmentproviding the electrical energy operated on by the at least one of theat least one external current transformer (CT) and the at least oneexternal potential transformer (PT), and a control unit controlling theequipment.
 24. The processing device according to claim 22, wherein theprocessing device generates control signals for controlling equipmentproviding the electrical energy operated on by the at least one of theat least one external current transformer (CT) and the at least oneexternal potential transformer (PT) for providing a selected input valuefor performing a test.
 25. The processing device according to claim 24,wherein the processing device determines the selected input value forperforming the test.
 26. The processing device according to claim 24,wherein the test comprises at least one of a first test includingtesting at least one test point in which the processing device controlsthe equipment for the input value to have a predetermined voltage; asecond test including a first series of test points in which theprocessing device controls the equipment for the input value to have adifferent predetermined current for respective test points of the firstseries of test points with the phase shift being zero degrees; and athird test including a second series of test points in which theprocessing device controls the equipment for the input value to have adifferent predetermined current for respective test points of the secondseries of test points with the phase shift being sixty degrees.
 27. Theprocessing device according to claim 26, wherein after testing a singletest point of one of the first series of test points and the secondseries of test points, the calibration factor corresponding to the atleast one error related to the input value used for the single testpoint is determined and uploaded.
 28. The processing device according toclaim 26, wherein after testing each of at least two test points of theone of the first series of test points and the second series of testpoints, the calibration factor corresponding to the at least one errorrelated to the input values used for the respective test point of the atleast two test points is determined and uploaded.
 29. The processingdevice according to claim 22, wherein: the at least one error isdetermined by performing a test, including measuring energy associatedwith a series of at least two test points; each test point of the seriescorresponds to a different input current value over a range of inputcurrent values of the electrical energy operated on by the at least oneexternal CT; for each test point of the series of at least two testpoints there is at least one corresponding calibration factor;respective calibration factors provide for adjusting measurement by themeter device, including correcting for errors of the at least one errorrelated to the input current values to which the respective test pointscorrespond; and the calibration factors corresponding to the respectivetest points compensate for non-linearity of the at least one errorassociated with the range of input current values.
 30. The processingdevice according to claim 29, wherein the greater the non-linearity ofthe at least one error associated with the range of input currentvalues, the greater the concentration of the series of at least two testpoints over the range of input current values.